A zero liquid discharge plant is an environmental engineering approach to the water treatment process that recovers fresh water from pollutants and solid wastewater while many water treatment processes maximize recovery and minimize waste zero liquid discharge is the most demanding target since the cost and challenges of recovery increase as the wastewater gets more concentrated. Saltness, spanning composites, and organics all increase in attention, which adds costs associated with managing these increases.

Table of Contents

ZLD is achieved by threading together water treatment technology that can treat wastewater as the pollutants are concentrated.

Zero Liquid Discharge Plant  ZLD in Bangladesh
Zero Liquid Discharge Plant / ZLD Structure

Zero liquid discharge plant is an advanced water treatment methodology that includes various types stage of wastewater treatment such as reverse osmosis, ultrafiltration, evaporation, and electro-deionization. which include more than 160 installations, membrane processes, hybrid systems including thermal/evaporative and stand-alone processes.

What is a zero liquid discharge treatment process?

Zero liquid discharge plants use advanced water treatment technology systems to limit liquid waste at the end of the industrial process so it’s called zero.

ZLD well-design system should be able to:

  • agree with required chemical volumes adjustments.
  • recover around 95% of your liquid waste for reuse.
  • produce a solid, dry cake for disposal.
  • create valuable water for your wastewater.
  • Manage waste contamination and flow.

Waste Water Chemistry

Careful consideration of wastewater chemistry is demanded the successful design and operation of a zero liquid discharge system. A sound water chemistry design base is crucial to a successful zero liquid discharge design.

The chemical ingredients of concern for a zero liquid discharge system generally are as follows

TDS/ TSSAlkalinity
COD/ TOC/ Duck Oil & Grease

Table 1 Typical Chemical Ingredients of Concern

In a zero liquid discharge system, the wastewater being reused is concentrated to the solubility limits of the dissolved mariners. When the solubility limits are exceeded, mariners solidify and can also be gathered using any applicable means.

Zero Liquid Discharge plant Technologies

  • Falling film brine concentrators
  • Forced circulation crystalizer
  • Horizontal spray film evoporator
  • Hybrid system with membrane pre-concentrators
  • Biological treatment
  • Solids waste handlin

ZLD Determining factors

  • The specific contaminants in the discharge stream
  • The volume of the dissolved material
  • The required design flow rate

Basic ZLD Design- ZLD Blocks

Despite the variable sources of a wastewater sluice, a ZLD system is generally comprised by two way which are represented.

ZLD Basic Blocks

Pre-Concentration;Pre-concentrating the brine is generally attained with membrane brine concentrators or electrodialysis( ED). These technologies concentrate the racecourse to a high salinity and are able to recover up to 60 – 80 of the water.

Evaporation/ Crystallization; The coming step with thermal processes or evaporation, evaporates all the leftover water, collect it, and drives it for reuse. The waste that’s left behind also goes to a crystallizer which boils all the water until all the contaminations shape and are filtered out as a solid.


Thepre-concentration of the liquid waste stream is a very important step due to the fact that it reduces the volume of the waste and downsizes significantly the very expensive evaporation/ crystallization step. generally it’s achieved with electrodialysis( ED) or membrane processes which consist of Forward Osmosis( FO) and Membrane Distillation( MD)( Figure 3).

Brine treatment technologies,( a) Electrodialysis,( b) Forward Osmosis,( c) Membrane Distillation

Electrodialysis/ Electrodialysis Reversal

Electrodialysis is a membrane operation that uses electrodes to produce an electric field which pushes negative and positive ions through semipermeable membranes with attached positively or negatively demanded species singly. ED is applied in multiple stages to concentrate the Neptune to achromatism situations. It’s constantly used together with RO for truly high water recovery. ED differs from RO because it removes the ions and not the water and vice versa for RO. Due to this fact silica and dissolved organics are not removed with ED which is important if the clean aqueduct is to be reused. ED requires solids, as does RO, solids and organics junking from the feed.

Electrodialysis reversal( EDR)

In EDR the opposition of the electrodes is reversed several times an hour and the fresh water and the concentrated wastewater are changed within the membrane mound to remove fouling and scaling.

Forward Osmosis

FO is an osmotic membrane process with a semipermeable membrane that unlike RO does n’t use usable pressure in order to attain separation of water from dissolved solutes like ions, molecules and larger bits. That means a lot lower of energy for the process in comparison to RO. In general FO uses thermal and electrical energy. Thermal energy can be substituted with low phase waste heat which can be set up far and wide in utmost artificial or near areas.

Membrane Distillation

MD is a thermally driven transport process that uses hydrophobic membranes. The driving force in the system is the vapor pressure difference between the two sides of the membrane pores, allowing for mass and heat transfer of the changeable result factors(e.g. water). The simplicity of MD along with the fact that it can use waste heat and/ or necessary energy sources, analogous as solar and geothermal energy, enables MD to be combined with other processes in integrated systems, making it a promising separation fashion.

The significance ofPre- attention in a ZLD Process

Thepre- concentration technologies have truly high recoveries but generally not enough like the typical thermal evaporation technologies to drive the brine into achromatism attention situations. So why are they so important? The reason is the CAPEX/ OPEX of the evaporators crystallizers. 1) Due to the sharp nature of the Neptune it takes more and more resistant essence composites in order to resist erosion as the attention rises. That means that the bigger is the evaporation/ crystallizer module, the bigger will be the CAPEX demanded( which can be 60- 70 of the whole process). 2) High energy demand due to the rise of the boiling point of the Neptune as attention goes advanced. Both points will be explained more analytically in the evaporation/ crystallization Lenntech webpages.

Electrodialysis/ Electrodialysis Reversal

Electrodialysis is a membrane process that uses electrodes to produce an electric field which pushes negative and positive ions through semipermeable membranes with attached appreciatively or negatively charged species independently. ED is used in multiple stages to concentrate the brine to saturation situations. It is frequently used together with RO for veritably high water recovery. ED differs from RO because it removes the ions and not the water and vice versa for RO. Due to this fact silica and dissolved organics aren’t removed with ED which is important if the clean racecourse is to be reused. ED requires solids, as does RO, solids and organics removal from the feed.

Why is Zero Liquid Discharge Important?

In a world where freshwater is an increasingly valuable resource, industrial processes threaten its availability on two fronts, unless the water is treated. Many industrial processes require water, and then reduce the availability of water for the environment or other processes, or alternately contaminate and release water that damages the local environment.

Another important reason to consider zero liquid discharge is the potential for recovering resources that are present in wastewater. Some organizations target ZLD for their waste because they can sell the solids that are produced or reuse them as a part of their industrial process. For example, lithium has been found in USA oil field brines at almost the same level as South American salars. In another example, gypsum can be recovered from mine water and flue gas desalinization (FGD) wastewater, which can then be sold to use in drywall manufacturing.

Regardless of an organization’s motivations to target zero liquid discharge, achieving it demonstrates good economics, corporate responsibility and environmental stewardship. By operating an in-house ZLD plant, disposal costs can be reduced, more water is re-used, and fewer greenhouse gases are produced by off-site trucking, which minimizes impact on local ecosystems and the climate. To learn more about implementing ZLD solutions, contact us.

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